1. Field of the Invention
The present invention relates to liquid ejection apparatuses, drive signal application methods, and liquid ejection methods.
2. Description of the Related Art
There are various types of liquid ejection apparatuses having elements that can execute an operation for ejecting ink, such as printing apparatuses, color filter manufacturing apparatuses, and dyeing apparatuses. In recent years, apparatuses with which a plurality of drive signals can be applied to a single element in order to broaden the range over which the amount of liquid that is ejected can be changed or to allow liquid to be ejected at higher frequencies have been proposed (for example, see JP 2000-52570A). With such apparatuses, a switch that controls the application of drive signals to the element is provided for each of the plurality of drive signals. Further, this apparatus is configured so that desired portions within each drive signal (i.e., a plurality of drive pulses included in each drive signal) can be selectively applied to the element. This allows the amount of ejected liquid to be selected variously.
To selectively apply a desired portion of a drive signal, selection data is set for each portion to be applied, and control is, performed based on the selection data (for example, see JP 10-81013A). In this apparatus, the selection data are stored on registers. The registers are configured of D-FF (delay flip flop) circuits, for example.
(1) Ordinarily, the above-mentioned registers store normal selection data. However, due to noise, for example, in practice there is also a possibility that abnormal data will be stored. For example, in the case of registers made of D-FF circuits, selection data are transferred to an adjacent register each time a transfer clock is input. If noise is propagated to the signal wire for the transfer clock, then this noise may be incorrectly recognized as the transfer clock. When noise is inadvertently recognized as the transfer clock, the registers will come to store selection data that are different from normal selection data. As a result, there is a possibility that a plurality of switches will enter the ON state simultaneously. When a plurality of switches enter the ON state simultaneously and there is a voltage difference between the drive signals, then there is a possibility that unanticipated current will flow and negatively affect the apparatus.
(2) Further, with the foregoing conventional apparatus, no special control is performed when switching between the drive signals that are applied to the elements. Thus, there is the possibility that a plurality of switches will be put into the ON state simultaneously at the timing at which the switches are switched. When a plurality of switches are in the ON state simultaneously and there is a voltage difference between the drive signals, a flow-through current can occur between a plurality of drive circuits. For example, there are instances where a current flows from a drive circuit that generates one drive signal and is drawn in by a drive circuit that generates an other drive signal. This flow-through current causes a sudden increase in current, for example, which may become a source of noise. There is a possibility that this noise will have a negative impact on, for example, the operation of the apparatus.
(3) Further, with the above-mentioned apparatus, a signal having a constant voltage is generated from the end of generation of one drive pulse to the start of generation of the next drive pulse. A control period is provided while this constant voltage signal is being generated. During this control period, a control for switching between applying and not applying the drive signal to the element is performed. With this apparatus, however, no special control is performed during this control period. As a result, there is a possibility that a plurality of switches may become on simultaneously at the timing at which the switches are switched. Consider a case in which the drive signal that is applied to an element is switched from one drive signal to another drive signal. In this case, the logic for switching the switch ON and OFF would be to switch the logic level corresponding to one drive signal from ON to OFF and switch the logic level corresponding to the other drive signal from OFF to ON. In practice, when trying to execute this control, the logic sometimes briefly fluctuates between ON and OFF during the transition period of this switching.
When a plurality of switches have simultaneously been put into the ON state and there is a difference in the voltage between the drive signals, then there is a possibility that an unexpected current will flow and have a negative influence on the apparatus. For example, there are instances in which a current flows from a drive circuit that generates one drive signal and is drawn in by a drive circuit that generates another drive signal. In other words, there are cases where a flow-through current occurs between a plurality of drive-circuits. This flow-through current causes a sudden increase in current, for example, which may become a source of noise. This noise may have a negative impact on, for example, the operation of the apparatus. This flow-through current also distorts the shape of the drive signals, and thus may also negatively affect the ejection of ink.
(4) Inkjet printers are known as one type of liquid ejection apparatus that ejects liquid droplets. With inkjet printers, ink droplets are ejected from nozzles provided in a head and land on paper, forming dots on the paper. Innumerable dots are formed on the paper to print a print image on the paper.
It is conceivable that the quality of the print image will be improved by changing the size of the dots that are formed on the paper. It goes without saying that forming a print image using dots of various sizes, such as large dots, medium dots, and small dots, will lead to a higher image quality than if dots of uniform size are used.
Forming dots of varying sizes, however, requires the size of the ink droplets that are ejected from the nozzles to be changed. To do this, it is necessary to apply various types of signals to the elements that are driven in order to eject liquid droplets. Conventionally, it has been necessary to provide a number of types of drive signals corresponding to the number of sizes of ink droplets to be ejected (see, for example, JP 9-11457A).
Increasing the types of drive signals, however, complicates the structure of the apparatus.